JP2012531099A - Cell reselection from macrocell to femtocell - Google Patents

Abstract

  The present invention discloses a method. The method includes storing identification or location information of a handover previously performed by the mobile system, predicting when the mobile system falls within the coverage area of the target femtocell, and identifying information or location information. And recognizing a coverage area based on the target area and scanning for a target femtocell before handover.

Description

  The present invention relates to the field of wireless communications, and more particularly to an apparatus and method for reselection from a macro cell to a femto cell.

  A mobile radio system allows users to communicate using a radio transceiver. Mobile radio systems include cellular telephone systems and personal communication service (PCS) telephone systems. Wireless transceivers include cellular phones, PCS phones, personal digital assistants (PDAs), and mobile internet devices (MIDs).

  Mobile radio systems are licensed from the government to access and use certain signal frequencies. Base stations are installed approximately every mile to support communication on licensed frequencies. The base station includes a cellular tower of a cellular network. However, due to constraints in voice and data transfer quality, rate, and range, the quality of service (QoS) of the licensed wireless system is lower than conventional wired (terrestrial communication lines) where user movement is constrained.

  Femtocells operate in licensed spectrum to connect standard mobile devices to a carrier network using broadband connections such as digital subscriber lines (DSL) and cable modems It is a low power wireless access point. Femtocells allow service providers to extend their service coverage indoors, especially where access is restricted or impossible.

  In a handover from a macro cell to a femto cell, since the macro cell base station currently notifies all mobile systems in the range, it is necessary to periodically broadcast system information of all neighboring base stations. The list of neighboring cells includes potential handover candidates that can be selected and redirected before handover.

  However, if a large number of femtocells coexist with a macrocell, such a protocol is not scalable. In particular, the current protocol consumes excessive battery power, resulting in excessive service interruption. Therefore, when the use of femtocells becomes widespread, a new solution for efficient handover is required.

4 is a flowchart illustrating cell reselection according to an embodiment of the present invention. FIG. 6 is a diagram illustrating scanning from a macro cell to a target femto cell, a handover trigger, and timing according to an embodiment of the present invention. FIG. 5 is a diagram illustrating a frame start offset that enables concurrent connection to a macro cell and a femto cell according to an embodiment of the present invention; FIG. 3 shows an apparatus for performing cell reselection according to an embodiment of the present invention. Table 1: MOB_FHO-REQ management message according to an embodiment of the present invention. Table 2: MOB_FHO-RSP management message according to an embodiment of the present invention. Table 3: Mobile system local FBS database according to one embodiment of the present invention.

  In the following description of the present invention, numerous details, examples and embodiments of the invention are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention is not limited to the details, examples, and embodiments described, and that the present invention may be practiced without the details, examples, and embodiments described. Can be implemented.

  In other instances, one skilled in the art will recognize that well-known details, examples, and embodiments are not specifically described so as not to obscure the present invention.

  Although various embodiments of the present invention are described in terms of a broadband wireless metropolitan area network (WMAN), the present invention is applicable to other types of wireless networks. Such networks may include, for example, wireless wide area networks (WWAN) such as wireless local area networks (WLAN), wireless personal area networks (WPAN), and portable networks.

  Furthermore, although a specific embodiment will be described with reference to WiMAX (Worldwide Interoperability for Microwave Access), the embodiment of the present invention is not limited to this, and other devices including a single carrier communication channel may be used as appropriate. It can also be implemented using a wireless interface.

  The following embodiments can be used in a variety of applications including wireless system transmitters and receivers. However, the present invention is not limited in this respect. Wireless systems within the scope of the present invention include network interface cards (NICs), network adapters, fixed or mobile client devices, mesh relays, base stations, gateways, bridges, hubs, routers, and other network equipment. It is not limited.

  Further, a wireless system within the scope of the present invention is a personal computer (computing device including a cellular wireless telephone system, a satellite system, a personal communication system (PCS), a bidirectional wireless system, a bidirectional pager, and a wireless system ( PCs, personal digital assistants (PDAs), mobile internet devices (MIDs), handheld communication devices, etc. and can be implemented in any system that is essentially related and to which the principles of the embodiments can be successfully applied.

  A femtocell is a device that combines a cellular base station (BS) and an access point. Femtocells are often small, lightweight, self-contained and inexpensive. In many applications, femtocells have reliable security and plug and play capabilities.

  Plug and play femtocells can be easily installed by users, not network operators. A femtocell can perform one or more functions, including automatic configuration, self-discovery (of the operator's network), self-authentication, self-registration, self-optimization, and automatic upgrade.

  In some applications, the femtocell may also perform auto-provisioning where the network prepares and equips the user for new services.

  In general applications, femtocells are placed indoors, such as SOHO (small office or home office), at the far end of the network, extending coverage to dead spots where radio waves do not reach due to location or building construction. Can improve. In operation, the femtocell can output a radio frequency (RF) signal with a transmission output of 10-300 m.

  If desired, the femtocell can provide simultaneous access to multiple unspecified user groups. Alternatively, simultaneous access can be limited to multiple specific user groups. In some cases, a group may include 1 to 60 users simultaneously.

  In addition to expanding and improving indoor coverage, femtocells can increase network capacity for mobile services that use large bandwidth, such as Internet browsing and video telephony. As an example, a peak data transfer rate of 8.75 MHz includes 20-40 Mbps downlink (DL) and 5-10 Mbps uplink (UL).

  Further, femtocells reduce congestion due to routing of IP (Internet Protocol) based services that do not place a load on the cellular network and return directly to the fixed infrastructure of the mobile carrier. For example, femtocells use existing wired broadband connections such as Asymmetric Digital Subscriber Line (ADSL), cable, Ethernet, or optical fiber for IP backhaul to the operator's core network Can do.

  A femtocell can relay a local connection to a macrocell in an external or outdoor cellular network when connecting voice, video, or data within a coverage radius. A macrocell typically has a base station (BS) outside the building where the femtocell is located. Both femtocells and macrocells operate in an operator licensed spectrum.

  Femto cells and macro cells may share frequencies or use different frequencies. When the macrocell and femtocell operate at the same frequency, the radio interface must support synchronization without much complexity.

  In a specific deployment, 1-1,500 femtocells may be placed within the coverage area of a macrocell. Preferably, adjacent femtocells should not interfere with each other. Femtocells must also coexist with other available connection technologies including WiFi and Bluetooth using unlicensed spectrum.

  In some cases, users include non-mobile devices such as notebook (laptop) computers and sub-notebook (netbook) computers. More generally, users include mobile systems (MS) such as mobile phones, personal digital assistants (PDAs), mobile internet devices (MID). Users often move slowly in buildings at about 3-4 miles per hour, which is a typical walking speed.

  Even when the user moves and the mobile system is transmitting and receiving signals, it is necessary to determine when and where it is best to initiate cell reselection before handoff or handover (HO). Delaying the handover can initially keep the cell capacity utilization high, but there is a risk of subsequent signal level and signal quality degradation.

  To maintain high quality of service (QoS), handover from a macro cell to a femto cell, from a femto cell to another femto cell, and from a femto cell to another macro cell needs to be efficient, reliable, and seamless . It is efficient if the femtocell uses a hard handover where the signal of the mobile system is completely transferred from the femtocell to another femtocell.

  However, if the femtocell uses a soft handover in which the mobile system is temporarily connected to two or more femtocells, the risk that the handover will not be successful can be reduced. In such a situation, the level and quality of signals from various femtocells are compared with each other, and a femtocell with good security, strong signal level, and high quality is finally selected.

  Cell reselection is generally a process prior to handover. Cell reselection is where the mobile system scans and associates one or more base stations to determine the eligibility of each base station as a handover target. During cell reselection, existing connections to serving base stations can be maintained.

  The present invention includes estimating when the mobile system falls within the coverage area of the target femtocell. In some embodiments of the invention, handover may be performed to the target femtocell using location-based information along with stored system information.

  Advantageously, according to some embodiments of the present invention, the use of location-based information along with stored system information to perform a handover can save energy of the mobile system and the bandwidth required by the cellular system Can be reduced. As shown in FIG. 1, the doctor selection process from the macro cell to the femto cell is generally performed before the handover.

  As shown in block 110 of FIG. 1, it is first determined whether the mobile system is likely to be within the range of the target femtocell. If the result is NO, the inquiry is repeated even while the mobile system is moving. If the result is yes, go to block 120 of FIG.

  Next, as shown in block 120 of FIG. 1, an on-demand or unsolicited unicast message may be sent.

  Next, as shown in block 130 of FIG. 1, it is determined whether DCD and UCD have been received.

  If the result is YES, proceed to block 170 of FIG. 1 to start the handover.

  However, if the result is NO, go to block 140 in FIG.

  Mobile system when the macro cell does not recognize the target femto cell because it was manufactured by a different vendor, or belongs to a network of different operators that do not have a mutual access contract, and the target femto cell cannot transfer the latest system information to the macro cell Before initiating a handover, it scans the channel using information in its local femtocell database (block 140), finds the latest system information for the femtocell (block 150), and uses the DCD from the target femtocell. A message and a UCD message are received (block 160).

  At block 110, a determination may be made based on information stored in the mobile system. For example, a mobile system stores identification (ID) information of macrocells that the mobile system has previously handed over to or from the target femtocell, such as in cache memory or buffer memory. Also good.

  As a result, each time the mobile system returns to the same macro cell, the mobile system recognizes the ID information of the macro cell, and based on this information, determines that the mobile station is within the range of the target femto cell.

  Alternatively, the macro cell may store location and / or network topology information that has previously been handed over to or from the target femto cell.

  As a result, each time the mobile system returns to the same macro cell, the macro cell recognizes the mobile system and based on this information, determines that the mobile station is within the range of the target femto cell.

  In other embodiments, the macrocell may be able to provide Location Based Service (LBS). The mobile system may store information of locations where the mobile system previously handed over to or from the target femto cell, if desired.

  Alternatively, the mobile system may determine the location using GPS (Global Positioning System).

  A WiMAX (Worldwide Interoperability for Microwave Access) client may obtain location information of the target femtocell using a location tracking device such as co-located GPS. As a result, each time the mobile system returns to the same location, it recognizes the location of the target femtocell and initiates a scan for that target femtocell before handover.

  As shown in block 120 of FIG. 1, an on-demand or unsolicited unicast message may be sent. For example, when the mobile system is expected to be within the coverage range of the target femtocell, the mobile system obtains the latest system identification (ID) information such as DCD (Downlink Channel Descriptor) and UDC (Uplink Channel Descriptor) of the target femtocell. The requested unicast message such as “MOB_FHO-REQ” can be transmitted to the macro cell. See Table 1 in FIG.

  In other cases, the mobile system may have previously acquired system identification information of the target femtocell when the user first installs the target femtocell. Generally, the system identification information is not changed. The unique identification information of the target femtocell is a 48-bit BS ID, an IP address, a host name, or a MAC address.

  When the macro cell receives the “MOB_SCN-REQ” message, it responds with “MOB FHO-RSP” and provides information for the mobile system to complete PHY and MAC synchronization during the cell reselection step. See Table 2 in FIG.

  Alternatively, without the mobile system first sending “MOB_SCN-REQ” to the macro cell, the macro cell sends an unsolicited “MOB FHO-RSP” message to the mobile system to the mobile system to the target femto cell. Notify to start preparation for handover.

  For example, when the mobile system is expected to fall within the coverage area of the target femtocell, the MOB FHO-RSP includes the latest system identification information such as DCD and UCD of the target femtocell in the mobile system before the handover. A non-requested unicast message may be transmitted. With the requested system identification information of the target femto cell, the mobile system can initiate PHY and MAC synchronization during cell reselection.

  In some situations, when a macrocell receives a unicast message from a mobile system requesting the latest system information of a target femtocell, it communicates with that target femtocell over the wired backbone and the requested target femtocell is requested. Get system information.

  In another situation, when a macro cell receives a unicast message from a mobile system requesting the latest system information of a target femto cell, the macro cell communicates with the target femto cell via macro cell radio communication and Get the requested system information.

  If the macro cell cannot obtain the latest system information of the target femtocell requested by the mobile system, the mobile system synchronizes with the target femtocell while maintaining the current service connection with the macrocell, and the mobile system's downlink control channel. Receive at.

  Mobile system when the macro cell does not recognize the target femto cell because it was manufactured by a different vendor, or belongs to a network of different operators that do not have a mutual access contract, and the target femto cell cannot transfer the latest system information to the macro cell Before initiating a handover, it scans the channel using information in its local femtocell database (block 140), finds the latest system information for the femtocell (block 150), and uses the DCD from the target femtocell. A message and a UCD message are received (block 160). See Table 3 in FIG.

  Referring to FIG. 2, in some embodiments of the present invention, when the mobile system 23 enters the coverage area of the macro cell 21 that overlaps the coverage area of the target femto cell, the macro cell 21 sends the mobile system to the target femto cell 22. 23 MAC (Media Access Control) context is transferred (210).

  Next, the target femtocell 22 starts monitoring uplink transmission of the mobile system 23 in the macrocell 21. This is possible when the target femtocell 22 periodically switches to the macrocell 21 client mode. This is because the target femtocell 22 is likely not fully loaded when it is expected to undergo a handover.

  Monitoring is performed at the PHY (Physical) layer, and the security layer is not seen. The target femtocell 22 listens to the common downlink (DL) control channel of the macrocell 21, receives the uplink (UL) transmission schedule of the mobile system 23, and receives the data burst correctly via the CRC (Cyclic Redundance Check). Verify that it can be done.

  When the target femtocell 22 detects that the mobile system 23 is within range, it notifies the macrocell 21 (230) and starts scanning or handover (240). In some applications, the target femtocell 22 and the macrocell 21 communicate via a wired backbone.

  In another application, the target femtocell 22 and the macrocell 21 communicate via wireless communication of the macrocell 21.

  Referring to FIG. 3, system information such as DCD and UCD is transmitted not in all subframes but only in certain subframes. In such a situation, the frame start time is offset by a certain number of subframes between the co-located macro cell 21 and the target femto cell 22, and the mobile system 23 is connected between the macro cell 21 and the target femto cell 22. The control information 210 from the macro cell 21 and the control information 220 from the target femto cell 22 can be received simultaneously before handover.

  FIG. 3 shows a frame including 8 subframes. The mobile system 23 switches from the macro cell 21 to the femto cell 22 only when there is no relevant information in the macro cell DL frame, as seen by DL control in the first DL subframe.

  As shown in FIG. 4, the present invention further includes an apparatus 400 such as a base station, access point, macro cell, pico cell, or femto cell that functions or operates in a network such as a wireless network.

  The apparatus 400 includes a radio frequency (RF) interface 410 and a processing unit 420. The processing unit 420 includes logic for executing the above process. This logic may include hardware, firmware, and software. The hardware can include circuitry.

  The RF interface 410 transmits and receives signals in various over-the-air (OTA) modulation or multiplexing schemes compatible with the above process. The RF interface 410 includes a receiver 412, a transmitter 414, and a frequency synthesizer 416. The RF interface 410 includes a bias control, a crystal oscillator, and one or more antennas 418, 419. The RF interface 410 may include an external voltage controlled oscillator (VCO), a surface acoustic wave (SAW) filter, an intermediate frequency (IF) filter, and a radio frequency (RF) filter.

  The processing unit 420 communicates with the RF interface 410 to transmit and receive signals. The processing unit 420 includes an analog / digital converter (ADC) 422 that down-converts a received signal, a digital / analog converter (DAC) 424 that up-converts a signal for transmission, and a PHY (physical) of a transmission / reception signal. And a baseband processor 426 for link layer processing.

  The processing unit 420 includes a processing circuit 428 that performs media access control (MAC) / data link layer processing. The MAC processing circuit 428 may include a scheduler 429 and a buffer memory 427. The processing unit 420 may include another interface 430.

  The PHY baseband processor 426 and the MAC processing circuit 428 function and operate to process the bandwidth request as described above. The PHY baseband processor 426 executes these processes independently of the MAC processing circuit 428. If desired, the PHY baseband processor 426 and the MAC processing circuit 428 can be integrated into a single processor or circuit.

  A number of embodiments and details have been described in order to provide a thorough understanding of the present invention. As will be apparent to those skilled in the art, many features of one embodiment are equally applicable to other embodiments. It goes without saying to those skilled in the art that these specific materials, processes, dimensions, concentrations, etc. described herein can be variously substituted in various equivalents. It should be understood that the detailed description of the invention is illustrative and not restrictive. The scope of the invention is determined by the appended claims.

Claims (20)

A method performed by a mobile system,
Storing information of a previous handover performed between the mobile system and a target femtocell;
Based on the information, predicting when the mobile system is once again within the range area of the target femtocell;
Recognizing the coverage area based on the information;
Scanning the target femtocell before performing handover again with the target femtocell.   The method of claim 1, wherein the information includes identification information of a macro cell that the mobile system has previously performed the handover to or from the target femto cell.   The method of claim 1, wherein the information includes location and / or network topology information where the mobile system previously performed the handover to or from the target femtocell.   The method of claim 1, wherein a macro cell and the target femto cell cooperate to exchange the information.   The method of claim 1, wherein a macro cell and the target femto cell cooperate to monitor the mobile system.   The method of claim 5, wherein the macro cell and the target femto cell communicate via a wired backbone.   6. The method of claim 5, wherein the macro cell and the target femto cell communicate via macro cell wireless communication. Predicting that the mobile system will fall within the coverage area of the target femtocell;
Transmitting a unicast message relating to the latest system identification information of the target femtocell.   9. The method of claim 8, wherein the mobile system transmits the unicast message as a requested unicast message to a macro cell requesting the latest system identification information of the target femto cell.   9. The method of claim 8, wherein a macro cell transmits the unicast message to the mobile system as an unsolicited unicast message that includes the latest system identification information of the target femto cell.   The method of claim 9, wherein the macro cell communicates with the target femto cell to obtain the latest system identification information of the target femto cell requested by the mobile system.   The method of claim 11, wherein the macro cell communicates with the target femto cell via a wired backbone.   The method of claim 11, wherein the macro cell communicates with the target femto cell via macro cell radio communication.   If the macro cell cannot acquire the latest system identification information of the target femto cell requested by the mobile system, the mobile system synchronizes with the target femto cell while maintaining a current service connection with the macro cell. 10. The method of claim 9, wherein the method is received on a downlink control channel of the mobile system. Offsetting the frame start time between the co-existing macro cell and the target femto cell;
Switching between the macrocell and the target femtocell;
Receiving control information from the macro cell and the target femto cell simultaneously.   The method of claim 15, wherein the system information is transmitted in certain frames instead of all frames.   The method of claim 15, wherein one frame has 8 subframes. A buffer memory storing identification information or location information of a handover previously performed by the mobile system;
And a logic for recognizing a coverage area of a target femtocell based on the identification information or the location information.   The apparatus of claim 18 further comprising a radio frequency interface.   The apparatus of claim 19, further comprising a PHY baseband processor and a MAC processing circuit.

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